Accessory spleen, Endoscopic ultrasound, neuroendocrine tumor
Accessory spleen or splenule is common and may be cause for potential misdiagnosis at EUS leading to unnecessary intervention. The case presented here demonstrates an incidental splenule mistaken for neuroendocrine tumor.
1.) Curved linear array echoendoscope (GFUC140P – Olympus Corp, Melville, NY)
2.) Electronic radial echoendoscope (GFUM160 – Olympus Corp, Melville, NY)
A 70 year old female was referred for evaluation of possible neuroendocrine neoplasm of the distal pancreas. The patient was incidentally found to have a possible pancreatic tail mass on CT imaging whilst undergoing evaluation for intermittent abdominal pain (previous diagnoses of irritable bowel syndrome). The patient had no prior history of excessive alcohol use, pancreatitis or alarm symptoms. Endoscopic ultrasound at another facility reported the presence of a 12.6mm x 9mm pancreatic tail mass; FNA was performed and preliminary cytopathology was suggestive of pancreatic neuroendocrine tumor.
Review of cytopathology at our institution was interpreted as polymorphous lymphoid tissue with no malignant cells or pancreas tissue identified. PET scan demonstrated no FDG (18F - Fluorodeoxyglucose) avid lesion within the pancreas and octreotide scan was negative. CA 19-9 and CEA were also normal.
Repeat EUS was performed by us with both radial and linear echoendoscopes to settle the question of a pancreatic tail lesion seen on outside EUS with anxiety and concern by the patient about having a pancreatic tumor. Initially a round to oval, 11 mm hypoechoic lesion with sharp, well defined borders was seen in the tail of the pancreas. Figure 1. Upon closer inspection the lesion was demonstrated to be inferolateral to the pancreatic tail and contiguous with the medial aspect of spleen (Figure 2) consistent with splenule or splenic lobulation. This is best appreciated on dynamic real time imaging (Video 1 and 2). Note similar echo attenuation between the questioned lesion and spleen. No other solid or cystic lesions were seen. The remainder of the pancreatic parenchyma was unremarkable without hyperechoic strands, lobulation, calcification or masses. The pancreatic duct was of normal caliber without stricture or dilation. No enlarged regional lymph nodes were seen. These findings were interpreted as consistent with splenule. No FNA or further intervention was deemed necessary.
Accessory spleen or splenule is a common congenital anomaly in which an ectopic focus of normal splenic tissue is found separate from the main body of the spleen. They occur in approximately 10% of the population1,2. In the majority of cases these are located at or near the splenic hilum. The pancreatic tail is also a common location for these lesions occurring in approximately 16% or 61 of 364 in a large autopsy series by Halpert and Gyorkey1 and 21.8% on large CT series3. Splenules may range in size from a few millimeters to several centimeters however they are most typically less than 2cm1,3. They are usually single but may be multiple. The majority are asymptomatic incidental findings usually on CT or ultrasound of the abdomen. Rarely, they may become symptomatic because of rupture, hemorrhage, torsion or cyst formation3. The primary clinical significance of these lesions resides in their mimicry of neoplasm.
Differentiation between splenule or splenic lobulation and neoplasm may be difficult. Previous cases of splenules masquerading as lymphadenopathy or tumors of the pancreas, adrenal gland, and kidney have been reported. In several instances unnecessary surgical resection has been performed. They may be a potential cause of misdiagnosis at EUS4. Previous investigators have attempted to characterize EUS features and develop criteria for the diagnosis of accessory spleen4. The lesions are typically homogenous appearing and round in shape with well demarcated regular outer margins. They do not always share the same echotexture as the spleen and may appear either hypoechoic or hyperechoic4.
EUS evaluation of splenic nodules near the pancreas requires close attention to the relationship of surrounding structures. Examination of the lesion from multiple planes with dynamic ‘real time’ imaging by linear and/or radial echoendoscope may be helpful. Their anatomic location may facilitate diagnosis, particularly with lesions in close proximity to the splenic hilum or tail of the pancreas. The most frequent location is posteromedial to the spleen3. Accessory spleens are generally not found superior and rarely found lateral to the main spleen3; the finding of such should suggest alternate diagnosis. Fine needle aspiration of indeterminate lesions is effective and may be necessary to confirm diagnosis5.
High quality CT may also facilitate diagnosis. Splenules are commonly detected as a solid enhancing mass on routine CT of the abdomen. It is noteworthy that these may enhance differently than the spleen on CT particulary when smaller than 1cm3. Lesions that do enhance similarly to the main spleen supports a diagnosis of splenule3. MRI and contrast enhanced ultrasound have also been used in the diagnosis of splenules. Nuclear scintigraphy studies (Tc99m sulfur colloid scan, radiolabeled heat-damaged red blood cells) may be helpful in distinguishing accessory spleen from tumor. Octreotide scan may facilitate diagnosis of neuroendocrine tumors. If the tests are equivocal and index of suspicion is high diagnositic laparotomy or laparoscopy may rarely be needed6. As this case report suggests, accessory spleen may be particularly difficult to differentiate from hypervascular pancreatic tumors such as neuroendocrine tumors. In this case, the endosonographer at outside institution considered the lesion in question to be within the pancreatic tail subjecting it to EUS FNA and with feedback to the cytopathologist of a small, well defined lesion in the pancreatic tail, the cytopathologist interpreted it as representing a neuroendocrine tumor in the pancreatic tail. This led to much anxiety on behalf of the patient regarding possible pancreatic surgery resulting in the patient coming to our tertiary cancer care hospital for clarifying the situation and seeking a second opinion.
1. Halpert B, Gyorkey F. Lesions observed in accessory spleens of 311 patients. J Clin Pathol 1959;32:165-8.
2. Davidoff S, Fernandes A, Sideridis K et al. Clinical challenges and images in GI. Intrapancreatic accessory spleen mimicking nonfunctioning neuroendocrine tumor. Gastroenerology 2006;131:350.
3. Mortele JK, Mortele B, Silverman SG. CT features of the accessory spleen. AJR 2004;183:1653-7.
4. Barawi M, Bekal P, Gress F. Accessory spleen: a potential cause of misdiagnosis at EUS. Gastrointest Endosc. 2000;52:769-72.
5. Fritscher-Ravens A, Mylonaki M, Pantes A, et al. Endoscopic ultrasound –guided biopsy for the diagnosis of focal lesions of the spleen. Am J Gastroenterol 2003;98:1022-7.
6. Lauffer JM, Baer HU, Maurer CA, et al. Intrapancreatic accessory spleen. A rare cause of pancreatic mass. Int J Pancreatol. 1999;25:65-8.